element.is('.class1, .class2')
works, but it’s 35% slower than
element.hasClass('class1') || element.hasClass('class2')

See also this jsbench.me test.
element.is('.class1, .class2')
works, but it’s 35% slower than
element.hasClass('class1') || element.hasClass('class2')

See also this jsbench.me test.